Punchy, not subtle tube sound

A Review On: HiFiMAN EF5 - Hybrid Headphone Amp

HiFiMAN EF5 - Hybrid Headphone Amp

Rated # 58 in Desktop Amps
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Price paid: $499.00
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Pros: tube mid range, good bass, power

Cons: stiff volume knob, warm up time

Although I've only had this about a week, I've decided to post since there is a dearth of posted reviews.

First about me;

prior gear I have had - Grado Headphone amp, Headroom Micro amp, Stax SR-5 headphones, Grado 325 headphones

current gear -Music Hall 25.2 headphone amp, Grado 80 headphones, Hifiman HE-400 headphones

biases - tube gear, planar and electrostatic speakers.... headphones used when I feel too lazy to fire up the main system.

Audiophile purchaser since the 80's


Packaging when received was plain cardboard box with foam cut outs to house the product, no issues there with

shipping protection. The 12AU7 tube provided was a generic Chinese tube which I promptly put back in the box along

with the generic IEC cable. IMHO using these stock components is basically wasting the money you spent for a better amp.

IEC used was 1M PS Audio Jewel power cable. Out of the box I started with an RCA clear top 12AU7, more or less a pleasant

fail safe starting 12AU7 for all tube gear.


On initial play the amp presented good characteristics but  was a bit aggressive and overly dynamic. So after 30 minutes of sampling

I put JRMC on repeat play to break in the amp. After 24 hours of play time things seemed to settle in so I began to do more serious listening.


12AU7 Tube rolling- I have Golden Lion, Siemens, Funkwerk, Prima Luna , Telefunken (ribbed), Mullard CV4003, RCA clear top, Electro Harmonix

The Telefunkens as always are the cleanest sounding but expose a bit of an aggressive edge in the highs. The Mullard CV4003's damped

that edge at the loss of some finer detail.  I spent the majority of time listening using the Mullards but will report back if further break in eliminates

the edge with the Telefunken or I find a better matching tube.


Listening musts: like most tube gear the amp required full warm up for best performance. I found that 1 hour was best to get to maximum background

detail clarity. Cable performance differences also mirrored my main system so this hopefully means that if you have cables you already like, they will

work well also with the EF-5 and not cause a frenzy of new cable auditions.


The sound: the best acronym to use describing the EF-5 is "pleasing". It has tube mid range, clarity, along with solid state bite, and power.

With the HE-400's I typically listened at around 1o'clock on the volume knob, and did not have to  use the +10db dip switches on the bottom

of the unit. The Grado SR80's sounded nice also with the amp but sounded like the cheaper headphones they are, stressed by the demand of the additional

detail presented. This suggests that you want headphones with good power handling capabilities, lesser headphones with good source won't be pretty.


Comparison: compared to the 2 headphone amps I have had and the Music Hall I still have, this is a clear winner. The Grado comes closest for midrange magic

but the battery powered version had no oomph, couldn't convince on transients. I wasn't happy with the Music Hall or the Headroom Micro headphone amp but have no desire to bash them.


Areas for improvement: there are basically 2 things (1) the volume knob is very stiff and the position indicator hard to see. A dot of white paint would be nice and perhaps some tension reduction for easier turning (2)  low volume detail playback seems slightly compromised. My gut suspicion is that the OPA275 is the cause. I'd love it if HifiMan worked with Dexxa on a discrete op amp alternative that could work with their case fit limitation.


believe i had a fullmusic tube on this ef5 when i had it, it powered the HE-5 beautifully.
i scotchtaped a strip of white paper onto the knob for easy view.
This amp is quite lightweight, when i stuck a hefty powercord on its tail-end, it kinda half-flipped into the air..lol.
I've played a bit more with this trying more out of it.  The op amp in the EF5 turned out to be an OPA275G which can be improved on in the OPA275 family. I put in a dual OPA275AU package which is working nicely, the punchiness is gone, much more natural sound and I can now use my favorite Telefunken 12AU7's with no edge from the amp. These cost about $55 at the supplier below
sorry, should have said OP627AU above, not OPA275AU
After doing a little more comparison, the basic difference between the OPA275G and the dual OP627AU op amps is that the former seems to concentrate its energy in whatever the loudest instrument is whereas the OP627AU has a closer to original reproduction of volume balance for secondary intstruments/ harmonics which is why the more natural sound. The only issue I have is that the OP627AU is more sensitive to bias voltage drift so that in between passages I can hear a barely audible sound like a kleenex being folded on left channel